We recently demonstrated that doublecortin-like kinase 1 (DCLK1) is a putative colorectal and pancreatic cancer stem cell marker. We also demonstrated that DCLK1 regulates multiple oncogenic and tumor supporting pathways and processes. Furthermore, siRNA mediated knockdown of DCLK1 results in growth arrest of pancreatic and colorectal cancer tumor xenografts. The DCLK1+ cell is now strongly implicated as a cell-of-origin for KRAS-driven pancreatic cancer, and recent proteomic studies demonstrate that knock-in of KRASG12/G13 mutations into CRC cells results in specific DCLK1 upregulation. Moreover, DCLK1 is highly expressed in CRC metastases and predicts significantly decreased survival in patients. The proposed studies for this application are related to two NCI-funded projects. 1. The role of DCLK1 in the initiation of pancreatic ductal adenocarcinoma. We will test our hypotheses with the experiments proposed in the following three specific aims: Aim 1: To determine the functional and molecular mechanisms through which Dclk1+ cells initiate pancreatic tumorigenesis. Aim 2: To delineate the multi-compartmental role of Dclk1 deletion in pancreatic tumorigenesis. Aim 3: To demonstrate the feasibility of targeting Dclk1 in PDAC as a therapeutic approach. 2. The role of DCLK1 in the initiation of colorectal cancer. We propose to unravel DCLK1's role in KRAS-mutant CRC progression and assess DCLK1-targeted therapies with the following Specific Aims: Aim 1: Determine the role of DCLK1 and the DCLK1+ tuft cell in the initiation and progression of KRAS-mutant colorectal cancer. Aim 2: Dissect DCLK1's mechanistic role in CRC downstream of KRASG12D and in the background of APC loss. Aim 3: Demonstrate the feasibility of targeting DCLK1 in KRAS-mutant patient-derived CRC models as a primary therapy and to overcome resistance to EGFR-targeted cetuximab and gefitinib. The current proposals include innovative genetically engineered mouse models of PDAC and CRC, innovative cell lines, and innovative concepts that may lead to translational studies on PDAC and CRC.